It's bug vs. bug in latest attempt to save ash trees

Michael Sears

Todd Johnson, a research intern working with UW-Madison entomologist Ken Raffa, releases the first parasitic wasps in Wisconsin at Riveredge Nature Center in Newburg on Wednesday. The wasps are being introduced to fight the emerald ash borer, an invasive pest that has killed millions of ash trees in the United States and was found in Wisconsin in 2008

By Lee Bergquist of the Journal Sentinel

Published on: 6/8/2011

Town of Saukville - Tiny parasitic wasps, Wisconsin's newest weapon in the war against the emerald ash borer, took flight Wednesday in a forest that is under siege from the invasive tree killer.

Two species of stingless Asian wasps that feast on the larvae of the emerald ash borer were released by scientists from the University of Wisconsin-Madison at the Riveredge Nature Center.

A third species that feeds on the egg stage of the bug will be introduced later this summer.

It was the first time that the wasps - which are invasive species in their own right - have been used in Wisconsin to battle the destructive beetle.

UW-Madison entomologist Ken Raffa and research assistant, Todd Johnson, released about 800 wasps from four plastic cups late Wednesday morning in a soggy, mosquito-ridden forest infested with the emerald ash borer.

The bug was first detected in the state in 2008 in nearby Newburg, where the skeletal remains of dead ash trees have become an all-too-common site.

Since then, they have been found in Cudahy, Franklin, Oak Creek, Green Bay, Kenosha and Victory in Vernon County.

Some chemical treatments have shown to be effective, including emamectin benzoate, according to a joint study by several Midwestern universities, including UW-Madison.

But chemical treatments are not feasible to protect entire forests.

The wasps arrived by mail on Tuesday from a federal breeding facility in Michigan, which is doling them out as a biological predator of the emerald ash borer.

The wasps parasitize the larvae and eggs of the insects.

Millions of trees lost

Emerald ash borer was discovered near Detroit in 2002 and has been responsible for the death of tens of millions of ash trees. The federal government has spent $282 million since 2002, according to federal figures.

The metallic green bug - whose larvae kill ash trees by interrupting the flow of nutrients beneath the bark - has spread from Quebec to Missouri.

To date, the state's most effective tools to fight emerald ash borer have been quarantine regulations limiting the movement of ash products in affected areas and a public relations campaign asking people not to move firewood around the state.

On Wednesday, after a rainstorm had passed, Johnson pulled the wasps from a cooler.

"They know what they have to do," Johnson said as he cajoled the one-tenth-inch wasps from cups. Many alighted on a black ash with a thinning canopy - a sure sign that the emerald ash borer was killing the tree.

Wisconsin becomes the 10th state to experiment with the use of wasps since 2007, when they were released in Michigan - the state hardest hit by emerald ash borer.

Nationally, about 165,000 wasps are being released this year - about the same number as 2010, according to federal authorities in Michigan.

The breeding stock was brought from China.

Ash trees there can defend themselves against ash borers. But there is no evidence that ash trees can defend themselves from the insect in the United States, Raffa said.

"The plan is for the wasps to be a self-sustaining drag on the emerald ash borer population," Raffa said.

"But we are not going to eradicate EAB - we're stuck with it. This darn pest is going to damage our forests."

The U.S. Animal and Plant Health Inspection Service approved the use of wasps in 2007, concluding that insects would not likely have an adverse effect on the environment.

Russ Davis is president and chief operating officer of Arborjet Inc., a Massachusetts-based company that makes equipment that injects chemicals into trees to control insects.

He supports the use of biological controls.

"But history has shown that they don't always work," said Davis, whose injection equipment is being used to treat ash trees for the City of Milwaukee.

Davis said he also worries about the length of time it will take for wasps to have an impact on the emerald ash borer, and the potential for unintended consequences.

The Asian lady beetle - a pest that looks like a native lady bug - first arrived in the U.S. in the early 1900s, but was reintroduced in the 1980s by southern farmers to control pecan aphids. Now it's found crawling into people's homes.